This invention relates to an arrangement for permitting a first liquid to flow close to a second liquid, but without being mixed therewith, in order, for example, to recover freshwater by distillation of sea water or to transfer heat from a relatively hot liquid to a relatively cold liquid. The arrangement is of a kind which comprises a first number of plates intended for the first liquid, and a second number of plates intended for the second liquid, which are located between, but separated from plates in the first number of plates. All plates are well separated from each other by means of special separating pieces located between each two of said plates.